Known in the past has been an internal combustion engine provided with a variable compression ratio mechanism which can change a mechanical compression ratio of the internal combustion engine. As such a variable compression ratio mechanism, various mechanisms have been proposed. As one among these, one which can change the effective length of a connecting rod used in the internal combustion engine may be mentioned (for example, PTLs 1 to 3). In this regard, the “effective length of a connecting rod” means the length between a center of a crank receiving opening which receives a crank pin and a center of a piston pin receiving opening which receives a piston pin. Therefore, if the effective length of a connecting rod becomes longer, a combustion chamber volume when the piston is at top dead center of the compression stroke becomes smaller, and therefore the mechanical compression ratio increases. On the other hand, if the effective length of a connecting rod becomes shorter, the combustion chamber volume when the piston is at top dead center of the compression stroke becomes larger, and therefore the mechanical compression ratio falls.
As described in PLTs 1 to 3, as a variable length connecting rod able to be changed in its effective length, there is known a connecting rod which moves a piston mechanism provided inside a connecting rod by hydraulic oil to change the effective length. In such a variable length connecting rod, to control the position of the piston mechanism and in turn the effective length of the connecting rod, it is necessary to control the flow of hydraulic oil supplied to the piston mechanism.
PLT 1 describes moving the position of a spool arranged in a hydraulic oil path formed inside of a connecting rod body so as to switch the direction of flow of the hydraulic oil. The spool is switched in its position by striking a cam disk arranged inside an oil pan at the time of rotation of the crankshaft. The position of the cam disk is controlled by an electric powered motor arranged inside the oil pan. By controlling the position of the cam disk, the position of the spool is switched and the effective length of the connecting rod is changed.